1. Field of the Invention
The present invention relates to a formant tone generating apparatus which is suitable for generating wind instrument tones, human voices (chorus) and the like including formant tones.
2. Prior Art
U.S. Pat. No. 4,200,021 (based on Japanese Patent Publication No. 59-19352) discloses an electronic musical instrument which generates a musical tone including the formant such as wind instrument tone, human voice and the like. This electronic musical instrument multiplies a periodic waveform as shown in FIG. 1(a) by a window function as shown in FIG. 1(b) to thereby produce a waveform as shown in FIG. 2, which is used as a tone element of the musical tone to be generated. Then, such tone element is periodically generated. In this case, the period of generating the tone element corresponds to a tone pitch, i.e., a pitch period of the musical tone. In order to maintain the formant at constant level, it is necessary to always maintain phase of a periodic waveform at constant phase.
The above-mentioned conventional instrument can generate the musical tone in desirable manner only when a pitch period T is longer than a time width Tw of the window function as shown in FIG. 2 or when T equals to Tw as shown in FIG. 3(a). In contrast, when the pitch period T is shorter than Tw as shown in FIG. 3(b), the conventional instrument is disadvantageous in that unnecessary spectrum is produced. In case of FIG. 3(b) where Tw&gt;T, next window function is started in the middle of certain window function, so that the unnecessary spectrum should be produced in a connection point between these two window functions. In other words, the conventional instrument cannot generate the high tone pitch because the pitch period T of which tone pitch can be generated is limited by the time width Tw of the window function.
In addition, the conventional instrument provides two waveform memories which store the periodic waveform and window function respectively. Then, data are read from these waveform memories in parallel, thereby forming the musical tone waveform. Therefore, the conventional instrument is disadvantageous in that its construction and control must be complicated.
Incidentally, as a method of producing two waveforms, "higher harmonic waveform generating method" is also known. However, even when such method is adopted, the construction must be complicated.